The proper design of a wheelchair seating system for either an adult or child requires that various locations of the user's body receive different degrees of support. For example, a number of seating systems exist which provide proportionally more support under a user's femoral region, and proportionally less support under a user's ischial tuberosities and coccyx. It is well known to provide support under a user in this manner so as to reduce support pressures on the user's ischial tuberosities and coccyx and distribute the user's weight much more evenly over the entire seating area, thus reducing the danger of the user developing localized pressure sores.
Designing optimal seating systems for child users of wheelchairs therefore presents unique problems for wheelchair seat designers as children constantly change in body size, shape and proportion as they grow. Accordingly, the particular parts of the child's body which require different amounts of support are constantly changing as the child grows. The child's growth also makes it difficult to design a seating cushion which also helps to center and balance the child, without the seating cushion requiring bucketing which becomes somewhat restrictive as the child grows.
One existing system for reducing pressure on a user's ischial tuberosities and coccyx is to provide a split-level support cushion underneath the user with a front raised area underneath the region of the user's femur bones, and a lowered back area at the back of the cushion positioned under the user's ischial tuberosities and coccyx. An example of such a system is found in U.S. Pat. No. 5,352,023 to Jay et al. which discloses a seating and back system for a wheelchair which is adjustable to accommodate the needs of a growing child. In this system, a downwardly rearwardly slanting step face is found between the raised femoral support region and the lowered ischial/coccyx support region of the cushion. The child's ischial tuberosities are preferably positioned against this step face, thus preventing the child from sliding forward along the seating surface, which otherwise would result in posture and spinal curvature problems. Ideally, the back of the child's knees are to be positioned immediately adjacent the front surface of the seating member in roughly a 90 degree orientation, such that the child's legs extend forward along the seating surface and then straight downward. The Jay system adjusts to accommodate the growth of a child by having one or more separate step members which can be inserted so as to move the slanting step face farther to the rear of the seating cushion as the child grows. By having such a step face, the location of which is adjustably movable back and forth, the child's ischial tuberosities can always be positioned against this step face, thus assisting in optimally holding and positioning the child upon the seating surface and avoiding problems caused by the child thrusting or scooting forward on the seat cushion. By moving the slanting step face rearwardly to ensure that the back of the child's knees are kept sufficiently close to the front end of the seat cushion as the child grows, the child's legs can remain angled downwards by 90 degrees in front of the cushion, such that the child's feet can comfortably rest on foot supports.
Unfortunately, some disadvantages remain with the Jay system. For example, the length of the cushion is itself not adjustable. This system, therefore, requires the child to be progressively seated farther and farther back upon the seating cushion as the child grows, to ensure that the back of the child's knees remain proximate the front end of the cushion. This feature of the Jay system requires the slanting step face to be moved farther and farther back along the seating cushion by adding step member inserts as the child grows. This in turn reduces the proportion of total surface area of the seating system which supports the user's ischial tuberosities/coccyx region, and increases the proportion of support area under the user'femoral region. The Jay system further necessitates an adjustable back system, which is movable backwards and forwards as required to maintain the proper substantially vertical alignment in the child's back.